Optical determination of the position of the stopper in glass ampoules

1. A method for determining a position of a stopper of a cartridge configured to be inserted in a pen medical apparatus along a travel distance, wherein the stopper comprises a front edge and a rear edge, the method comprising the steps of:

generating light by a light source on a first side of the cartridge, wherein the cartridge comprises a pierceable seal;

fixing the stopper movably along the travel distance towards the pierceable seal of the cartridge, the stopper movable along the travel distance by being functionally connected to a plunger stem;

providing a photosensitive sensor surface on a second side of the cartridge opposite the first side;

generating a silhouette of the stopper on the sensor surface by irradiating the stopper with light from the light source; and

converting the data relating to the silhouette by a data processing unit into the position of the stopper along the travel distance, wherein converting the data relating to the silhouette into the position of the stopper along the travel distance comprises:

determining which one of a first cartridge region, a second cartridge region, and a third cartridge region the stopper is located in, wherein the first cartridge region comprises a cartridge end region, wherein the third cartridge region comprises a cartridge shoulder region, and wherein the second cartridge region comprises a cartridge region residing between the first cartridge region and the third cartridge region;

using the determination as a basis to decide between different ways of determining the position of the stopper, and

determining, in accordance with the decision, the position of the stopper,

wherein the data processing unit uses the position of the front edge but not the position of the rear edge to determine the position of the stopper if the determination is that the stopper is in the first cartridge region,

wherein the data processing unit uses the position of the front edge and the position of the rear edge to determine the position of the stopper if the determination is that the stopper is in the second cartridge region, and

wherein the data processing unit uses the position of the rear edge and not the position of the front edge to determine the position of the stopper if the determination is that the stopper is in the third cartridge region.

2. The method as claimed in claim 1 , wherein the stopper comprises a stopper of a cartridge for a pharmaceutical and the pharmaceutical comprises insulin.

3. The method as claimed in claim 1 , wherein the data processing unit is integrated in the medical apparatus.

4. The method as claimed in claim 1 , wherein a separate data processing unit is operated together with the medical apparatus.

5. The method as claimed in claim 1 , wherein the light source consists of an LED row.

6. The method as claimed in claim 5 , wherein the LED row gives a diffuse beam.

7. The method as claimed in claim 5 , wherein the individual LEDs of the LED row have a small aperture angle.

8. The method as claimed in claim 5 , wherein a converging lens is inserted between the LED row and the stopper.

9. The method as claimed in claim 8 , where the converging lens is a cylindrical lens.

10. The method as claimed in claim 1 , wherein the light source generates red light.

11. The method as claimed in claim 1 , wherein laser light is generated by at least two light sources aligned side by side.

12. The method as claimed in claim 11 , wherein red laser light is generated.

13. The method as claimed in claim 1 , wherein the sensor surface consists of a row of arranged sensor elements.

14. The method as claimed in claim 13 , wherein the sensor elements consist of a CCD line-scan camera.

15. The method as claimed in claim 14 , wherein a sensitivity is greatest with red light.

16. The method as claimed in claim 13 , wherein a sensitivity is greatest with red light.

17. The method as claimed in claim 1 , wherein when the data processing unit determines the position of the stopper using the position of the front edge and the position of the rear edge, a maximum measurement error of the position of the stopper corresponds to half the width of a pixel of the photosensitive sensor surface.

18. A device for determining a position of a stopper of a cartridge configured to be inserted in a pen medical apparatus along a travel distance, wherein the stopper comprises a front edge and a rear edge, this device comprising at least:

a light source provided on a first side of the cartridge, wherein the cartridge comprises a pierceable seal;

a plunger stem functionally connected to the stopper and configured to fix the stopper movably along the travel distance towards the pierceable seal of the cartridge;

a photosensitive sensor surface provided on a second side of the cartridge, opposite the first side; and

a data processing unit configured to convert data relating to a silhouette of the stopper into the position of the stopper along the travel distance, wherein converting the data relating to the silhouette into the position of the stopper comprises:

determining which one of a first cartridge region, a second cartridge region, and a third cartridge region the stopper is located in, wherein the first cartridge region comprises a cartridge end region, wherein the third cartridge region comprises a cartridge shoulder region, and wherein the second cartridge region comprises a cartridge region residing between the first cartridge region and the third cartridge region; and

using the determination as a basis to decide between different ways of determining the position of the stopper,

wherein the data processing unit is configured to use the position of the front edge but not the position of the rear edge to determine the position of the stopper if the determination is that the stopper is in the first cartridge region,

wherein the data processing unit is configured to use the position of the front edge and the position of the rear edge to determine the position of the stopper if the determination is that the stopper is in the second cartridge region, and

wherein the data processing unit is configured to use the position of the rear edge and not the position of the front edge to determine the position of the stopper if the determination is that the stopper is in the third cartridge region.

19. A medical apparatus which is suitable for administering a pharmaceutical into the human or animal body, avoiding the gastrointestinal tract, comprising a device according to claim 18 .

20. A medical apparatus according to claim 19 wherein the pharmaceutical is insulin.